1. Field of the Invention
The present invention generally relates to the field of medical devices, and more particularly to a system for stabilizing a portion of a spinal column. In an embodiment, the system joins together adjacent spinous processes to stabilize a portion of a spine.
2. Description of Related Art
Spinal instability may result from many factors including trauma or degenerative disorders stemming from injuries and/or aging. In some instances, the effects of spinal instability may result in pain and/or partial or complete loss of mobility.
Several devices and techniques have been developed to restore stability to the spine. For example, interbody devices may be implanted within a prepared disc space to replace all or a portion of a damaged or compressed disc. To support the spine, vertebrae adjacent to a damaged or defective disc may be fused to each other with an interbody device or with interbody devices. In some instances, interbody devices alone may not be capable of supporting a portion of a spine sufficiently to promote vertebral fusion. A separate stabilization system may be required to improve stability of the spine or a portion of the spine.
One method of providing spinal stabilization utilizes a pedicle screw system. A pedicle screw system may stabilize one vertebra by connecting the vertebra to a second vertebra using anchoring pedicle screws and/or connecting rods or plates. The connecting rods or plates may extend between the vertebrae. Pedicle screws are generally installed in pairs for each vertebral level that requires fixation. A pedicle screw is typically inserted into a pre-bored hole at the junction of a superior articular process and transverse process through the pedicle. A pedicle screw may be inserted in a craniolateral to caudomedial direction, depending on the particular region of the spine being stabilized.
Pedicle screw insertion is a technically demanding surgical procedure for spinal stabilization due to the close proximity of the spinal cord canal and/or major blood vessels. Complications may occur during the installation or use of pedicle screws for spinal stabilization or immobilization. Complications may include neural or dural damage as a result of pedicle screw penetration into the spinal canal or intervertebral foramen, pedicle screw bending and/or pedicle screw breakage. In addition, pedicle screw insertion may require highly invasive surgery. Such surgery may result in extended recovery times or even irreparable damage to adjacent tissues. Pedicle screws may be angulated in a craniolateral to caudomedial direction, depending on placement within the spine. Angulation of the pedicle screws may require a large exposure of the spine during insertion to accommodate desired trajectories of the pedicle screws.
Spinal stabilization may be established using braces attached to vertebrae. The braces may provide flexion/extension immobilization of the vertebrae. The braces may include plate systems positioned adjacent to the spine. Generally, plate systems are comprised of two opposing plates positioned on opposite sides of vertebral spinous processes. The plates may vary in size to accommodate variations in spinal anatomy.
To couple the plates to vertebrae, spinal plate systems may utilize nut and bolt assemblies positioned in pre-drilled holes in the plates. In some systems, the bolts are positioned in the space between the spinous processes of adjacent vertebrae. These systems may depend on a compressive force applied to the lateral sides of the spinous processes by the opposing plates to hold the system to the vertebrae.
U.S. Pat. No. 5,527,312 issued to Ray, which is incorporated by reference as if fully set forth herein, describes a system incorporating a facet screw anchor and fixation bar for immobilizing two vertebrae relative to each other. A portion of a fixation bar is wrapped around a portion of a superior vertebra pedicle. The fixation bar is secured to a facet screw anchor and the facet screw anchor is positioned through a facet joint of the superior vertebra and into the base of a transverse process of an inferior vertebra. The fixation bar and facet screw immobilize the superior vertebra and the inferior vertebra.